Method and apparatus for stabilizing productive formations



1961 A. B. HILDEBRANDT 2,998,065

METHOD AND APPARATUS FOR STABILIZING PRODUCTIVE FORMATIONS 2Sheets-Sheet 1 Filed Jan. 9, 1957 FIG.'2

FIG?! Alexander B. Hildebrondt Inventor Byw, Ahorney 1961 A. B.HILDEBRANDT 2,998,065

METHOD AND APPARATUS FOR STABILIZING PRODUCTIVE FORMATIONS 2Sheets-Sheet 2 Filed Jan. 9, 1957 FIG-4 FIG-3 Alexander B. Hildebrand:Inventor y '10. $7M t y 2,998,065 METHOD AND APPARATUS FOR STABHJIZINGPRODUCTIVE FORMATIONS Alexander B. Hildebrandt, Tulsa, Okla., assignor,by

mesne assignments, to Jersey Production Research Company Filed Jan. 9,1957, Ser. No. 633,268 7 Claims. (Cl. 166-15) The present inventionrelates to the completion of wells in unconsolidated sand formations andmore particularly relates to an improved method and apparatus for thecompletion of wells whereby the sand particles in an unconsolidatedproducing formation are supported under pressure from within the wellbore in order to prevent their entrainment in fluids flowing from theformation into the well.

The production of oil, gas or water from a well drilled into anunconsolidated sand formation is usually accompanied by numerousdifliculties arising from the entry of particulate solids into the wellbore. This sand not only tends to fill and clog the well but is alsoentrained in the fluids pumped to the surface, causing excessive wear onpumps, liners and other equipment, increased pumping costs, and addedexpense due to the necessity for separating the sand from the fluids.Sand production often leads to the undermining of large areassurrounding the borehole and the caving in of the overlying strata. Whenthis occurs, the production tubing is usually badly bent or collapsedand it is necessary to stop production of the well and repair thedamage. Frequently the well must be abandoned. Even if the productiontubing is not damaged, caving of the overlying strata may permit theentry of foreign fluids into the producing reservoir or, in the case ofgas wells, permit substantial quantities of gas to escape into higherreservoirs outside the producing area of the well.

Various methods designed to reduce sand production and thus alleviatethese problems have been proposed from time to time and several suchmethods are currently in use. The most successful of these involves theplacement of a bed of gravel or similar material around a perforatedpipe or liner at the end of the production string in order to filter thesand particles from the producting fluids and prevent their entry intothe well bore. A related practice is to use a fine screen as a filter inplace of the gravel pack. Plastic consolidations which can be applied tothe borehole walls and then perforated have also been used for thispurpose.

None of these methods for controlling sand production has been foundcompletely satisfactory. Filter media cannot be made fine enough to holdback all of the sand without being subject to excessive clogging. Gravelpacks, screens and similar devices are therefore designed to admit thesmaller particles into the borehole while filtering out the larger ones.Under these conditions the size of the openings in the filter mediumbecomes critical and the selection of the proper screen or gravel tominimize sand production is diflicult. A change in the production rateof the well or other conditions may result in complete disruption of thefiltering action, permitting the influx of large amounts of sand.Screens are generally short-lived unless they are 'made of expensivealloys because of corrosion and the eroding action of the entrained sandparticles. Plastic consolidations partially seal the formation,decreasing the production rate, and are frequently ruptured by thepressure created by the producing fluids. For these and similar reasonsthe control of unconsolidated formations remains an acute problem andcollapsed production strings are quite common even though gravel packs,screens, plastic consolidations and the like are used.

atent It has now been discovered, however, that unconsolidated sandformations can be effectively controlled by the application of force tothe walls of the borehole within the formation, thus creating pressureswhich counteract the pressures tending to break down the formation andcause entrainment of sand particles in the producing fluids. Thesepressures should be substantially equal to but not in excess of theoverburden pressure. It has been found that the frictional forcesbetween individual sand particles under such pressures are suificientlyhigh to hold the particles in place over large unsupported areas and 'toprevent sand entrainment even though fluids flow from the formation intothe borehole at high velocities. By positioning a porous producingmedium in the borehole and expanding or otherwise forcing the mediumagainst the formation so that the sand particles are retained in theiroriginal undisturbed position, sand production and the diflicultiesassociated therewith can thus be virtually eliminated.

The porous producing medium utilized in accordance with the inventionmay comprise an expansible perforated sleeve or liner, a bed of gravelor similar granular material, a tapered production liner, or a bed ofmetallic burrs or the like which can be forced into the formation andinterlocked. The size of the openings or free spaces in the medium isless critical and can be larger than in the case of conventionalscreens, gravel packs and the like. It has been found that under theconditions employed in accordance with the invention unconsolidatedsands will bridge across unsupported areas 50 grain diameters or more inwidth, whereas in conventional well completion operations the openingsmust not exceed about 2 /2 times the diameter of the smallest particleit is desired to exclude. The particles remain firmly in place eventhough fluids flow from the formation into the well at high velocities.The use of such a relatively coarse medium in conjunction with pressureagainst the borehole wall does not appreciably restrict the flow offluids or reduce the production rate of the well.

A preferred means for creating pressure against the unconsolidated sandformation in accordance with the invention involves the expansion of atubular member in the bottom of the borehole by the hydrostatic pressureof a column of liquid maintained above a packer positioned on the,production string. In lieu of using such an expansible member, a pistonmay be formed above a granular producing medium and the weight of theannulus fluid used to compress the medium and force it outward againstthe formation. In certain instances the weight of the production stringmay be utilized to exert pressure against the formation.

The exact nature of the invention can be more clearly understood byreference to the accompanying drawings, in which:

FIGURE 1 shows in sectional elevation one means for controlling sandproduction in accordance with the invention whereby a perforated sleeveis expanded against the formation; Wk

FIGURE 2 depicts a further embodiment of the invention whereby a tubularmember is expanded against a gravel pack in order to create thenecessary pressure;

FIGURE 3 is a sectional elevation showing yet another embodiment of theinvention which is adapted for use in well bores wherein considerablewashout has occurred during the drilling operation; and,

FIGURE 4 shows an embodiment of the invention adapted for use inrelatively thin unconsolidated sand formations.

Referring now to FIGURE 1, reference numeral 1 represents a well borewhich has been drilled down through various subterranean formations 2into an unconsolidated producing formation 3 containing oil, gas orwater, or a mixture of these fluids. Casing 4 has been set and cementedin place in the well, the cement being designated by reference numeral5. A string of tubing 6 carrying a producing element as described belowhas been loweredin the well into the unconsolidated producing formation.

Connected to .the lower'end of tubing 6 is collar 7 having multiplepassages 8 extending therethrough parallel to the bore'of thecollar.Packer 9 is athxed to the collar. surface and may be of the cup or liptype as shown in the drawing or instead may be of the bottomholetypewhich is expanded in place againstthe borehole wall or casing by thetelescoping of internal sleeves in response to the weight of theproduction string. Packers set in place against the borehole wall by therotation of the production string may also be used.

Such packers are widely'used in drilling operations and methods fortheir incorporation into the apparatus used in the present inventionwill be apparent to those skilled in the art. Production tube It isconnected to the lower bore of collar 7 and expansible sleeve 11'isattached to the lower outside edge of the collar surrounding theproduction tube. The sleeve and production tube are joined at the bottomby shoe 12 to form an annular compartment into which fluids may beintroduced through passages 8 in collar 7. Production tube 10 and sleeve11 contain corresponding holes or perforations spaced evenly over thesurfaces thereof and each hole or perforation in the production tube isconnected to a corresponding hole or perforation in the sleeve by meansof a flexible connecting tube 13. The connecting tubes are affixed influid-tight relationship to the walls of the production tube andsleeveand are coiled or looped to permit expansion of the sleeve awayfrom the production tube. Sleeve 11 may be made of relatively thincopper, lead, aluminum, Teflon or similar material and may be corrugatedin order to permit maximum expansion. In lieu of using coiled or loopedconnecting tubes, telescoping tubes having -ring or similar seals may beemployed; The producing element may be of any desired size but beforeexpansion should have a diameter only slightly less than the diameter ofthe well casing and will preferably beof sufficient length to extendsubstantially through the producing formation. 7

After the producing element described above and shown in FIGURE l-hasbeenpositioned at the bottom of the borehole, water, drilling mud orasimilar liquid isintroduced into the annulus of theborehole. It is preferred-that water be used as the annulus fluid. The annulus liquid flowsdownward through passages 8 in collar 7 and fills the annular spacebetween the production tube and sleeve 11. As a column of liquid isbuilt up in the annulus of the borehole, the hydrostatic head of thisliquid causes sleeve 11 to expand outward against the unconsolidatedsand formation, creating pressure against the formation. Theintroduction, of the annulus liquid is continued until. the pressure atthe bottom of the column is substantially equal to the overburdenpressure. Sleeve il-bears against the sand and holds the particlesfirmly in place in substantially their original undisturbed position.Producing fluids vflow from the formation into the openings in thesleeve, through the connecting tube, and into the production tube, fromwhich they are withdrawn to the surface. The sands bridge across theopenings in the sleeve and are not swept into the producing element.

In the embodiment of the invention shown in FIGURE 2, a gravel pack isused as the producing medium and a tubular sleeve is expanded againstthe gravel pack to create the necessary pressure. As shown in thefigure, the borehole has been drilled down through. overlying formations14 into unconsolidated producing formation 15 and casing 16 has been setin place with cement 17. A string of tubing 13 has been lowered in thehole.

Attached to the lower end of tubing =18 is connecting member19 havingtwo fluid passages therethrough, a first passage "20 connecting tubing18 with the annular section of the borehole below the connecting memberand a second passage 21 connecting the annular section of the boreholeabove the connecting member with a perforated tube 22 connected to theunderside of the connecting member. A packer 23 which is preferably ofthe lip or cup type, although other types may be used, is positioned onthe outer surface of the connecting member 19. Perforated tube 22 issurrounded by an expansible sleeve 38 and is connected thereto at thebottom by a shoe 24 containing a port 25 fitted with a ball or similartype valve 26.

Following the placing of the expansible sleeve and associatedequipmentin the borehole, a gravel pack 27 I is placed around the sleeveby entraining gravel or other suitable granular material in a drillingmud or other liquid introduced into tubing 18 at the surface; The liquidand entrained gravel flow downward through the tubing and passage 20 inthe connecting member into the annular space surrounding the expansiblesleeve. The gravel is deposited around the sleeve and the entrainingliquid passes through port 25, pressure of the circulating liquidholding open the valve. The liquid then flows up ward through perforatedtube 22 and passage 21 in the connecting member into the annular sectionof the borehole above the connecting member and packer. During thedeposition of the gravel pack the pressure differential inside andoutside the sleeve is not sufiicient to cause deflection of the sleeve.After the gravel pack has been placed, water is pumped downward throughthe production string in order to wash away the mud left behind.

To expand the sleeve and thus create the required pres of this columncauses the sleeve to expand outwardagainst the gravel pack, which inturn exerts pressure against the formation. The sand particlesbridge'across the free spaces in the 'gravel pack and are retained inplace. 'Fluids flowing from the formation pass upward around the sleeveand flow through the connecting member and tubing to'the surface.

FIGURE 3 depicts a further embodiment of the invention which isparticularly adapted for use in boreholes wherein considerable washouthas occurred during drilling and the diameter of the borehole Within theunconsolidated formation is too large or irregular to permit use of theapparatus described heretofore. After the borehole has been drilled downthrough the overlying strata 28 into the unconsolidated reservoir 29 andeasing 3i) and cement 31 are in place, a string. of tubing 32 havingconnected thereto a perforated production tube 33 is lowered into thewell. The production tube is sealed at the bottom and may consist merelyof a length of pipe or tubing with a plurality of holes, slots or otheropenings cut at regular or irregular intervals. A gravel pack 34 isplaced around the production tube by circulating a gravel-laden drillingmud or other liquid downward through the annulus of the borehole andwithdrawing the liquid, free of gravel, through the tubing to thesurface. Water is then circulated through the borehole to washanyremaining drilling mud from the formation and the gravel pack. a

After the gravel pack has been placed in the borehole and washed free ofdrilling mud, a piston is created above the gravel pack by. introducingsuccessively finer grades of gravel, said, silt or other solid materialuntil an impervious layer several feet thick has been built up. Binderssuch as bentonite and other clays, greases andsimiIar materials may beadded to the finer grades of solid material used to form the piston inorder to insure that it will be impervious to the passage of liquids. Acolumn of water, drilling mud, or other liquid is then introduced intothe annulus of the borehole. The weight of the liquid on the pistoncompresses the gravel pack and forces it outward against the formation,creating the necessary pressure. Producing fluids pass through thegravel pack and into the production tube, from which they are withdrawnto the surface.

In comparatively shallow formations the apparatus of FIGURE 4 may beemployed to permit the control of unconsolidated sands in accordancewith the invention. After the borehole has been drilled into the sandformation, a tapered reamer is used to extend the hole further into theproducing sands. A tapered production liner 36 is then lowered into thehole at the end of a string of tubing 37. The Weight of the tubing onthe liner creates s-uflicient pressure against the formation to retainthe sand particles in place as fluids flow from the formation into theliner and thence to the surface. In particularly soft unconsolidatedformations it is frequently unnecessary to ream out the hole, the weightof the production string being adequate to force the liner into theformation to the desired depth.

As will be apparent to those skilled in the art, a variety of methodsmay be employed in order to create pressure against an unconsolidatedsand formation and thus prevent the entrainment of sand particles influids produced from the formation in accordance with the invention.Regardless of the particular method employed, it is preferred that thepressure created be substantially equal to the overburden pressure,although in some formations less pressures will be required than inothers because of ditferences in the size and shape of the particles"making up the formation.

It will be understood that the apparatus disclosed herein is merelyrepresentative and that numerous modifications in the exact proceduresdescribed may be made without departing from the scope of the invention.

The nature of the invention having thus been disclosed and illustrated,what is claimed is:

l. A well completion method for controlling sand production in a wellbore drilled into an unconsolidated producing formation which comprisesplacing a porous medium in the well bore adjacent to the producingformation, continuously forcing said medium against said formationduring production of said well with a force suflicient to create apressure against said formation substantially equal to but not in excessof the overburden pressure, and conducting fluids from said formationthrough said medium into a production string extending to the earthssurface.

2. A well completion method for preventing the influx of sand particlesinto a well bore from an unconsolidated formation while conductingfluids from said formation through a production string to the earthssurface which comprises placing a particulate porous medium in the wellbore adjacent to the producing formation, maintaining a column of liquidin the annulus of the well bore above said producing formation wherebysaid medium is forced against the formation with a pressuresubstantially equal to the overburden pressure, and conducting fluidsfrom the formation through said medium into the production string withsaid column of liquid being maintained while said fluids are beingconducted from said formation.

3. An apparatus for controlling sand production in a well bore havingits lower portion tapered and drilled into an unconsolidated producingformation which comprises: a production string adapted to be positionedin a well bore; and a tapered, perforated production liner attachable tosaid string, said tapered production liner substantially matching saidtapered borehole, the weight of said drill string forcing said linerdownwardly against said tapered borehole to retain the sand particles inplace.

4. A well completion method for preventing the influx of sand particlesinto a well bore from an unconsolidated formation while producing fluidsfrom said formation through a production string having a tapered,perforated liner attached to the lower end thereof to the earths surfacewhich comprises: forming a tapered cone shaped hole in said formation tosubstantially match said tapered liner; and forcing said linerdownwardly during production of said well with a force suflicient toforce said tapered liner against said producing formation with a forcenormal to the borehole wall substantially equal to the overburdenpressure.

5. An apparatus for controlling sand production in a well bore drilledinto an unconsolidated formation in which casing has been set to atleast the upper portion of said formation and a tubular productionstring has been suspended within said casing which comprises incombination: a production tube having perforations in its wall and of acharacter to connect to the lower end of said production string in afluid tight relationship; an expandable sleeve member surrounding saidproduction tube and having spaced perforations in its wall; tube meansfluidly and sealingly connecting each perforation in the production tubeto a corresponding perforation in the sleeve; packing means sealing thelower annular space of said well bore between said production string andsaid casing; and means establishing fluid communication between theannular space above said packing means and the space between saidproduction tube and said sleeve not occupied by said connecting tubemeans.

6. A well completion method for preventing the influx of sand particlesinto a well bore from an unconsolidated formation while conductingfluids from said formation through a production string to the earthssurface which comprises: plaoing a particulate porous medium in the wellbore adjacent to the producing formation; depositing an impervious layerof finely divided solids above said porous medium between saidproduction string and said casing; maintaining a column of liquid in theannulus of the well bore above said impervious layer while producingfluids from the formation through said medium into the production stringwhereby said porous medium is forced against the formation with apressure substantially equal to the overburden pressure.

7. An apparatus for controlling sand production in a well bore drilledinto an unconsolidated formation in which casing has been set to atleast about the upper portion of said formation and a tubular productionstring has been suspended within said casing which comprises incombination: a packer means sealing the annular space between the lowerend of said production string and said casing; a perforated tubesupported from and sealingly attached peripherally at its upper end tosaid packer means; an expansible sleeve surrounding said perforated tubeand the upper end of said sleeve peripherally attached in sealingrelationship to said perforated tube; means to close the lower end ofsaid perforated tube and said expansible sleeve; a first passage in saidpacker means establishing fluid communication between the interior ofsaid tubular production string and the exterior of said expansiblesleeve below said packer means; and a second passage in said packermeans establishing fluid communication between the annular space abovesaid packer means between said production string and said casing and theinterior of said perforated tube.

References Cited in the file of this patent UNITED STATES PATENTS602,547 Titus i Apr. 19, 1898 2,167,190 Vietti July 25, 1939 2,796,134Binkley June 18, 1957 2,814,347 MacKnight Nov. 26, 1957 2,848,052Stinson r Aug. 19, 1958

